WASHINGTON — As the House Ethics Committee opened what it said would be a broad but expeditious inquiry into the Mark Foley scandal, the embattled House speaker, Representative J. Dennis Hastert, accepted responsibility for the handling of the matter but again rejected calls to relinquish his leadership position.

The ethics committee Thursday promised to conduct its inquiry into the salacious messages from Foley to young House pages as quickly as possible - "in weeks, not months," a Democratic member said - and it subpoenaed four dozen documents and witnesses.

At the same time, Hastert spoke to reporters from a microphone-covered podium outside his hometown office in the Chicago suburb of Batavia. "I'm deeply sorry it happened," he said, before adding that, "ultimately, the buck stops here."

But to shouted questions about when he had first learned of Foley's troublesome exchanges with pages, Hastert insisted that answers would come only when the ethics committee, the Justice Department and Florida authorities concluded their investigations.

"Republicans dealt with it immediately and the culprit is gone," he said. "We're now trying to correct the problem." But asked about accounts that his aides knew of the problem as early as 2003, he said, "I don't know who knew what when."

Hastert said that he was working to make it harder for any future lawmaker to have inappropriate contacts with pages and former pages. He announced the creation of a hotline that pages and their families could use to report questionable behavior.

The speaker also said he was looking for someone to study ways to make the page system safer. Hastert did not confirm a CNN report that he wanted a former FBI director, Louis Freeh, to fill that role.

Representative Doc Hastings of Washington, the Republican chairman of the ethics committee, pledged to pursue the investigation "wherever the evidence leads us." He would not say whether Hastert was among those subpoenaed.

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While the committee has power to subpoena Foley, it cannot punish him since he is no longer a member of Congress. The senior Democrat on the panel, Representative Howard Berman of California, said that "we are looking at weeks, not months," but would not say whether the panel's work might be completed before the Nov. 7 elections. He and other committee members said the matter would be handled fairly and with gravity.

Hastert has said in a series of interviews that his resignation would only help Democrats, who hope to take control next month of at least one House of Congress. But the spectacle of bitter Republican infighting has done the party's candidates no good, making it harder for them to make their campaign messages heard.

On Wednesday, Kirk Fordham resigned as chief aide to Representative Tom Reynolds, Republican of New York. Fordham, previously a Foley aide, said that he had asked Hastert's staff before 2004 to help stop Foley's contacts with teenagers. Scott Palmer, Hastert's chief of staff, denied Fordham's version. Reynolds, a Republican leader whose own re-election may be imperiled, defended Fordham.

"He felt that his existence as my chief of staff would be a distraction," Reynolds said. "He's done nothing wrong."

Representative John Boehner of Ohio, the majority leader; Representative Roy Blunt of Missouri, the whip; and Reynolds, who heads House re-election efforts, have all either questioned Hastert's version or said they would have responded more vigorously.

It has been an extraordinary political parade of criticism, particularly given Republicans' loyalty to a man of whom The New York Times wrote in 2001 that "no one has gone to the mat more for President Bush than Representative J. Dennis Hastert." The White House has done its best to stay out of the matter. When Tony Snow, the White House spokesman, was asked Thursday about the investigation, he sought to portray a president removed from the details.

But the other House leaders, in detaching themselves from Hastert or his version of the Foley story, appear to view the speaker increasingly as a weight around the ankles of Republicans struggling to keep control of both houses of Congress.